The CV121 is a directly heated high voltage high vacuum half wave rectifier. The 19H1 is the commercial equivalent but the V1920 was the prototype.
The pressed metal anode is carbonised to radiate more heat and so allow the valve to run cooler. The construction is rugged.
The anode end on showing the rounded and ridged structure. The side flanges add to the surface area and provide for the support rods.
The twin inverted V oxide coated filaments and their tension springs. The top insulator is substantial ceramic. The copper anode connection is seen on the left.
The detail of the construction is made clear in this image. Note the ceramic item at the top of the inside of the anode. This is not easy to see or its function clear but may exist to hold the filament at the centre of the cavity. Also visible is the fact that the filament is actually coiled.
Inspection shows that the anode is formed in two pieces. Small valves would have the anode formed from a single sheet that was stamped and then folded. The lower ceramic sits just above the pinch.
The wide glass tube envelope is 51 mm in diameter and, excluding the B4 base pins, is 171 mm tall.